Abstract
Selenium, an essential trace element, is co-translationally incorporated into selenoproteins as the 21st amino acid selenocysteine. Selenite serves as an inorganic selenium source for selenoprotein biosynthesis through reduction to selenide, which is converted to selenophosphate, the essential selenium donor in selenocysteyl-tRNA[Ser]Sec synthesis. However, the pathways for selenite reduction in mammalian cells have not yet been clarified. Based on metabolic labeling with [75Se]selenite and RNA silencing studies, we here present evidence that thioredoxin reductase 1, but not thioredoxin, is crucial for selenite utilization to form selenoproteins in HeLa cells. We suggest that thioredoxin reductase 1 plays a role as a selenite-reducing enzyme in vivo.
